In cathode ray tube display systems of the type generally used in television receivers and computer monitors, one or more electron beams within the cathode ray tube are scanned horizontally and vertically with respect to a phosphor coated faceplate to define a raster. In general, the vertical or top to bottom direction scan is substantially slower than the horizontal or left to right direction scan. The picture or video information to be displayed is used to intensity modulate the beam or beams within the CRT to form a displayed image.
The proper image display requires that the intensity modulation of the cathode ray tubes with video or picture information be properly timed to the horizontal and vertical scan process. In most systems, a plurality of horizontal and vertical synchronizing signals generally referred to as "sync" are included within the image bearing signal during the transmission process or in other signal production processes such as computer generated video or the operation of video cassette recorders. Within the television receiver or computer monitor, the reference horizontal and vertical synchronizing signals are separated from the remainder of the signal and used to synchronize or properly time the horizontal and vertical scan processes.
Because the basic operations of television and computer monitor scan systems are generally similar, manufacturers often endeavor to provide a single scan system which is operable in both television receivers and computer monitors. Unfortunately, while this is economically desirable, several problems must be overcome to provide such a multi-use scan system. For example, broadcast or cable television signals utilize a single horizontal sync frequency while computer monitors operate using a variety of horizontal scan frequencies. In addition, television related devices such as video cassette recorders and video game units often generate horizontal sync signals which are subject to substantial frequency and phase deviation. In addition, such devices are also subject to excessive noise problems which contaminates the sync signal and further exacerbates the problem of horizontal scan synchronization. Finally, the general character and quality of the sync signal produced by such varied devices is also subject to variation.
Notwithstanding the problems inherent in such multiple use scan synchronizing systems, there remains nonetheless a continuing need in the art for effective, reliable and cost effective multiple use scan systems.
Accordingly, it is a general object of the present object of the present invention to provide an improved multisync horizontal drive generator. It is a more particular object of the present invention to provide an improved multisync horizontal drive generator which readily functions in response to a variety of sync signal quality and frequency characteristics .